1. Field of the Invention
The present invention relates generally to an air jet loom and, more particularly, to a picking controller for an air jet loom, for automatically controlling picking conditions for groups of subnozzles, such as jet pressure and jet duration, so as to be at optimum values.
2. Related Art
An air jet loom is provided, for picking a operation, with a main picking nozzle and groups of subnozzles. The main picking nozzle is disposed near a selvedge of a fabric on the picking side of the air jet loom mainly to drive a weft yarn at an initial running speed, and the groups of subnozzles are arranged along the running path of a weft yarn to help the picked weft yarn run further and to regulate the dynamic position of the picked weft yarn.
The jet pressure of the subnozzles more directly influences the running mode of the picked weft yarn than that of the main picking nozzle. For example, when the jet pressure of the subnozzle is insufficient, the picked weft yarn meanders unstably and is unable to extend properly along the running path, because the subnozzles are unable to apply a sufficient conveying force to the picked weft yarn. Consequently, a bent pick or a kinky filling results, and an arrival phase angle of the crankshaft of the loom at which the picked weft yarn arrives at an arriving position varies between picking cycles.
Under such circumstances, it has been a usual practice to set the jet pressure of the subnozzle at a value higher than that considered to be appropriate to secure stable running of the picked weft yarn in anticipation of the variation of the shape of a supply package and the variation of the physical properties of the weft yarn. Accordingly, the conventional air jet loom consumes an unnecessarily large amount of compressed air.
For example, an invention disclosed in Japanese Laid-Open Patent Publication No. 60-110952 simultaneously controls both the jet pressure of the main picking nozzle and that of the subnozzles so as to maintain the jet pressure of the main picking nozzle and that of the subnozzles in a fixed relationship, to thereby regulate the running time of the picked weft yarn so as to occur at a fixed time. However, the influence of variations in the condition of the running path, such as soiling of the reed, on the running mode of the picked weft yarn can be cancelled simply by controlling the jet pressure of the subnozzles. Nevertheless, this prior art invention necessarily changes the jet pressure of the main picking nozzle simultaneously with the jet pressure of the subnozzles so as to thereby waste compressed air, which is undesirable in view of saving energy.
An invention disclosed in Japanese Laid-Open Patent Publication No. 60-162838 measures the running speed of a picked weft yarn indirectly through the detection of variations in the amount of a stored weft yarn, and automatically controls the respective jet pressures and respective jet timings of the main picking nozzle and the subnozzles on the basis of the indirectly measured running speed of the weft yarn. However, a detector provided on the picking side is unable to accurately detect the running mode of the picked weft yarn, particularly, the dynamic position of the picked weft yarn. Accordingly, this prior art invention also is incapable of accurately controlling the jet pressure of the subnozzles.